Yield point of metallic glass Original Research Article

Shear bands form in most bulk metallic glasses (BMGs) within a narrow range of uniaxial strain εy ≅ 2%. We propose this critical condition corresponds to embryonic shear band (ESB) propagation, not its nucleation. To propagate an ESB, the far-field shear stress τ∞ ≈ Eεy/2 must exceed the quasi-steady-state glue traction τglue of shear-alienated glass until the glass transition temperature is approached internally due to frictional heating, at which point ESB matures as a runaway shear crack. The incubation length scale linc necessary for this maturation is estimated to be ∼102 nm for Zr-based BMGs, below which sample size-scale shear localization does not happen. In shear-alienated glass, the last resistance against localized shearing comes from extremely fast downhill dissipative dynamics of timescale comparable to atomic vibrations, allowing molecular dynamics (MD) simulations to capture this recovery process which governs τglue. We model four metallic glasses: a binary Lennard-Jones system, two binary embedded atom potential systems and a quinternary embedded atom system. Despite vast differences in the structure and interatomic interactions, the four MD calculations give εy predictions of 2.4%, 2.1%, 2.6% and 2.9%, respectively.